For example, in a manufacturing process of a semiconductor device or a liquid crystal device, a substrate is subjected to a process such as etching, sputtering, CMP (Chemical Vapor Deposition) or the like. In those processes, a plasma processing apparatus using plasma is widely used. In the plasma processing apparatus, a processing gas is injected into a processing chamber accommodating the substrate and, then, the processing gas is converted to plasma and activated, so that each of the above-mentioned processes is performed on the substrate.
Hereinafter, various plasma processing apparatuses are explained specifically. FIG. 17 shows a parallel-plate dual-RF (Radio Frequency) type plasma etching apparatus 101 which generates capacitively-coupled plasma (CCP) by using a RF electric field formed between both electrodes. The plasma etching apparatus 101 includes a processing chamber 102 as a vacuum chamber, a mounting table 103 for mounting thereon a wafer W and serving as a lower electrode within the processing chamber 102, and a gas shower head 105 having a plurality of gas supply holes 104 and forming a ceiling plate of the processing chamber 102.
Sidewalls of the processing chamber 102 are made of, e.g., aluminum, and inner surfaces of sidewalls are covered and insulated with a ceramic such as yttrium oxide (Y2O3) or alumite (Al2O3) or the like. Moreover, within the sidewalls there are coolant flow channels 106 circling along the sidewalls to control a temperature thereof.
The gas shower head 105 is provided at its lower side with an upper electrode 107 which includes a metal base 108 made of, e.g., aluminum, and a conductive plate 109 made of, e.g., silicon, which is located on a lower surface of the metal base 108. Although not shown in FIG. 17, within the metal base 109, there are coolant flow channels to control a temperature of the gas shower head 105.
A reference numeral 110 in FIG. 17 refers to a gas supply source which supplies the gas shower head 105 with processing gas which, in turn, is supplied to the wafer W through the gas supply holes 104. A reference numeral 111 in FIG. 17 refers to a gas exhaust line which exhausts the gas in the processing chamber 102, thereby bringing the pressure of the chamber 102 into a predetermined value. Reference numerals 112, 113 in FIG. 17 refer to first and second RF power supplies respectively. If each of the first and second RF power supplies 112, 113 turns on after the processing gas has been supplied to the processing chamber, a RF power of, e.g., 13 MHz to 60 MHz from the first RF power supply 112 is applied to the upper electrode 107 to generate plasma under the upper electrode 107 as shown in a dotted line of FIG. 17 and activate the processing gas, and at the same time, a RF power of, e.g., 0.38 MHz to 13 MHz from the second RF power supply 113 is applied to the mounting table 103 to generate a biasing potential which attracts ions in the plasma toward the wafer W to etch the surface of the wafer W.
In the plasma etching apparatus 101, the gas shower head 105 and the processing chamber 102 are made of metal materials and have the coolant flow channels to cool down them, so that the temperatures of the gas shower head 105 and the processing chamber 102 can be controlled. Accordingly, even when a plurality of wafers W of a same lot is processed sequentially, temperature increasing due to accumulated heat in each sequential process can be avoided. As a result, processing variations on the wafer W due to the heat from the gas shower head 105 and the processing chamber 102 can be avoided. Further, even when, e.g., a processing gas whose components are readily deposited in a high temperature level is used, deposition of the components can be suppressed by controlling the temperatures of the gas shower head 105 and the processing chamber 102. Consequently, it is possible to suppress the likelihood that deposits become particles to contaminate the wafer W.
Following is a description of a plasma etching apparatus 120 as shown in FIG. 18. The plasma etching apparatus 120 generates plasma by using microwaves. In FIG. 18, for elements or units having the same configuration as those of the plasma etching apparatus 101 shown in FIG. 17, the same reference numerals are used. A reference numeral 121 in FIG. 18 refers to a first gas supply unit which forms a ceiling plate of a processing chamber 102 and is made of a ceramic of, e.g., silicon oxide (SiO2) or Al2O3 or the like so as to transfer microwaves to a lower surface thereof as will be explained later. The first gas supply unit 121 also forms a gas shower head. Provided in lower parts of the first gas supply unit 121 are first gas supply holes denoted as a reference numeral 122. A reference numeral 123 refers to a gas supply source for supplying a plasma generating gas. The gas supply source 123 supplies the plasma generating gas 122 into the processing chamber through a gas path 124 provided within the first gas supply unit 121 and, then, the first gas supply holes 122.
A reference numeral 125 in FIG. 18 refers to a second gas supply unit which partitions the space between the first gas supply unit 121 and a mounting table 103, and also forms a gas shower head. The second gas supply unit 125 includes a plurality of second gas supply holes 126. A reference numeral 127 refers to a gas supply source for supplying a processing gas such as an etching gas or a depositing gas. The processing gas supply source 127 supplies the processing gas toward the wafer W through a gas path 128 provided within the second gas supply unit 125 and, then, the second gas supply holes 126. A reference numeral 129 refers to through-holes penetrating through the second gas supply unit 125 so as to supply the etching gas from the first gas supply unit 121 toward the wafer W.
A reference numeral 131 in FIG. 18 refers to a microwave generating unit which supplies microwave having a frequency of, e.g., 2.45 GHz or 8.3 GHz. The microwaves move through a transfer unit 132 and the first gas supply unit 121, and, then, are emitted toward a processing space under the first gas supply unit 121, so that the plasma generating gas from the first gas supply unit 121 is converted to plasma as shown by a dotted line of FIG. 18. Thereafter, the plasma-converted plasma generating gas goes down and, then, converts the processing gas supplied from the second gas supply unit 125 to plasma, so that the plasma-converted processing gas processes the surface of the wafer W.
Following is a description of a plasma etching apparatus 141 as shown in FIG. 19A. The plasma etching apparatus 141 generates inductively-coupled plasma (ICP) and includes a processing chamber 142 made of quartz. Reference numerals 143, 144 in FIG. 19A refer to nozzles for supplying a processing gas. As shown in FIG. 19B, a coil 145 winds around upper portions of the processing chamber 142. One end of the coil 145 is connected to a RF power supply 112 and the other end thereof is connected to ground. If an electric current is applied to the coil 145 after the processing gas has been supplied from the nozzles 143, 144, an electric field is generated in the processing chamber 142 to generate plasma as shown by a dotted line in FIG. 19A.
However, because in the parallel-plate electrode type (capacitively-coupled type) plasma etching apparatus 101 of FIG. 17, the RF power is applied directly between the upper electrode 107 and the mounting table 103 serving as the lower electrode, the electron temperatures in the plasma in the apparatus 101 of FIG. 17 becomes increased to, e.g., 3 eV to 4 eV compared with the microwave plasma etching apparatus 120 or the inductively-couple plasma etching apparatus 141. Accordingly, in the etching apparatus 101, ions or the like having a high level energy collides with the wafer W, which may cause significant damage to the wafer W.
Additionally, in the etching apparatus 101, there appear interferences of the two RF powers, since the plasma generating RF power is applied to the upper electrode 107 serving as a ceiling plate of the processing chamber, and, at the same time, the biasing RF power is applied to the mounting table 103 serving as the lower electrode. As a result, a waveform of the RF power applied to the mounting table 103 is distorted, and, hence, it is difficult to control the RF power. Moreover, this is reason why variations of energy distribution of ions in the plasma on the surface of the wafer W occur. On the other hand, such variations can be controlled to be negligible by adjusting parameters such as frequency, power level and the like of each of the RF power supplies 112, 113. However, because this approach will need to control as many parameters as possible, not only it will take long time but also many parameters must be fixed for suppressing the variations, thereby decreasing the degree of freedom in the plasma processing. Moreover, a shape of ion collision distribution where a horizontal axis represents an ion energy level and a vertical axis represents a collision frequency of ions against the substrate corresponds to a shape of the waveform of the biasing RF power if the biasing RF power does not interfere with the plasma generating RF power when the biasing RF power is applied to the mounting table 103. Thus, an adequate shape of the ion collision distribution shall be selected based on the processing process. However, when the biasing and plasma generating RF powers interfere with each other, such a selection will be not performed with a good precision.
To solve the above problem, a gap between the upper electrode 107 and the mounting table 103 can be as large as possible. However, in this approach, the plasma itself may not be generated, making it impossible to perform the normal processing.
On the other hand, in the microwave plasma etching apparatus 120 of FIG. 18, the microwaves emitted from the ceiling plate do not interfere with the biasing RF power applied to the mounting table 103 and, hence, the waveform of the biasing RF power applied to the mounting table 103 is not distorted. Further, the electron temperature beneath the first gas supply unit 121 becomes as high as 5 eV to 10 eV, whereas the electron temperature near the wafer W becomes as low as 1 eV to 2 eV. This is because the processing gas near the wafer W is converted to the plasma by actions of the plasma generating gas supplied from the first gas supply unit 121. Accordingly, the energy of ions or electrons acting toward the wafer W is low, so that the wafer damage by the plasma can be suppressed.
However, in the microwave plasma etching apparatus 120 of FIG. 18, the first gas supply unit 121 forming the ceiling plate of the apparatus 120 is made of the ceramic so as to effectively transfer the microwaves to the lower surface thereof, but it is difficult to control the temperature of the first gas supply unit 121. This is because a heat capacity of the ceramic is larger than that of a metal such as aluminum or the like. Therefore, when a plurality of the wafers W within the same lot is processed sequentially, the heat from each sequential process is accumulated onto the first gas supply unit 121. As a consequence, the accumulated heat makes an influence on the processing of the wafer W, which may cause processing variations between wafers. In addition, as mentioned above, when, e.g., the processing gas whose components are readily deposited in a high temperature level is used, the deposits of the gas become particles to contaminate the wafer W.
Further, in the microwave plasma etching apparatus 120 of FIG. 18, an inner space of the processing chamber 102 becomes vacuum state during the processing and, hence, a diffusibility of the processing gas increases. For this reason, it is likely that some of the processing gas supplied from the second gas supply unit 125 does not diffuse toward the wafer W but diffuses into a space near the first gas supply unit 121 through the through-holes 129, and, then, turns back toward the wafer W. Further, as mentioned above, the electron temperature near the first gas supply unit 121 is higher than the electron temperature near the wafer W. Accordingly, a dissociation level at which molecules of the processing gas are dissociated into ions or radicals, an energy level and, hence, a reaction level with the wafer W are different between the processing gas supplied directly from the second gas supply unit 125 onto the wafer W and the processing gas that is supplied from the second gas supply unit 125 and diffuses into the space near the first gas supply unit 121, and, then turns back toward the wafer W. In conclusion, wafer in-plane variations and/or wafer to wafer variations of the processing may occur.
Further, in the inductively-couple plasma etching apparatus 141 of FIG. 19A, a RF current is not applied directly into the processing chamber 142 and, hence, the waveform of the RF power supplied to the mounting table 103 is not distorted. However, because a heat capacity of the quartz is larger than that of a metal such as aluminum or the like, it is difficult to control the temperature of the processing chamber 142 made of the quartz. Accordingly, the heat from each wafer processing is accumulated into the sidewalls and the ceiling plate of the processing chamber 142. As a consequence, there may occur the wafer to wafer processing variations in the same lot as in the microwave plasma etching apparatus 120. In addition, as in the microwave plasma etching apparatus 120, when, e.g., the processing gas whose components are readily deposited in a high temperature level is used, the deposits of the gas become particles to contaminate the wafer W.
Further, in the inductively-couple plasma etching apparatus 141, an electric field is generated in an upper part of the processing chamber 142 and, hence, it is impossible to supply the processing gas by using the gas shower head. For this reason, the processing gas is supplied from nozzles in the etching apparatus 141. Thus, it is difficult to uniformly supply the gas on the wafer W, so that wafer in-plane uniformity in the etching process decreases.
In conclusion, each of the above-mentioned plasma processing apparatuses has at least one among defections including the difficulty to control the temperature of the sidewalls and the ceiling plate of the processing chamber, the substrate damage by the plasma, the non-uniformity of the gas supply to the substrate, and the difficulty to control the waveform of the RF power.